The present invention relates generally to a gas turbine engine system and a method of operating the same.
A typical gas turbine engine provides a generally axial flow of fluids through the engine, with those fluids entering a forward inlet of the engine and exiting an aft exhaust outlet while following a path that always extends generally rearward. Radial flow engines, for example where air is diverted in a direction perpendicular to an engine centerline, are also known. However, reverse-flow gas turbine engines are also known where a primary flowpath of the engine “reverses” whereby a portion of that flowpath is turned so as to travel forward through the engine before being turned again to exit a generally aft portion of the engine.
Gas turbine engines, whether of the axial flow, radial flow, or reverse flow variety, generally use shafts to rotationally link different sections of the engine (e.g., a low pressure compressor section and a low pressure turbine section). Rotationally linked sections are commonly referred to in the art as “spools”.
Different engine sections have different operational efficiencies. Engine core efficiency increases with temperature and pressure. Engine propulsors (fans) become more efficient at lower pressure ratios and become more efficient at relatively low power levels (i.e., relatively low throttle levels), while engine cores (e.g., a higher pressure section of the engine including a compressor section, combustor, and turbine section) typically operate at relatively high efficiency at relatively high power levels with high temperatures and pressures (i.e., relatively high throttle levels). Because different sections of prior art gas turbine engines are bound to some fixed rotational relationship (e.g., a given throttle setting produces a given operational power level from both the fan section and the core), different engine sections have countervailing operational minimums. This results in a tradeoff. In the aerospace context, an aircraft's gas turbine engine(s) will generally have relatively low fan efficiency and relatively high core efficiency during takeoff (or other relatively high throttle conditions), and have relatively high fan efficiency and relatively low core efficiency for cruise (or loiter) conditions (or other relatively low throttle conditions).
In some applications, thrust augmenters (e.g., afterburners) are provided to allow for additional thrust at selected times in a flight envelope. Thrust augmenters are used, for example, to assist with supersonic flight and for maneuverability. However, known thrust augmenters like afterburners are relatively fuel inefficient. Inefficiencies for thrust augmenters also arise from the need to adjust pressure ratios of other sections of an engine to less than optimal levels (for those sections in isolation) in order to permit proper functioning of the thrust augmenter (e.g., afterburner).